1. Field of the Invention
The present invention relates to a recording apparatus which uses a recording head and to the processing of recording data.
2. Description of the Related Art
In recent years, there has been a rapid implementation of multi-color and multi-nozzle technologies in ink jet printing apparatuses to obtain higher image quality and speed. Consequently, efforts have been made also with respect to the recording data so that a large amount of data can be transferred to the recording head at high speed.
FIG. 5 shows a control configuration of a recording data transfer for the purpose of transferring a large amount of data to the recording head at high speed. FIG. 6 shows a storing format of the recording data (refer to U.S. Pat. No. 6,793,312).
As shown in FIG. 5, the recording data stored in a recording buffer 105a is temporarily stored in a static random access memory (SRAM) (1) 106 in a 16-column unit. The recording data are generated by the various printing modes. The recording data are then transferred column by column to a recording head (constituted of 128 nozzles in FIG. 5).
The recording data transferred to the recording head 1 are controlled by a block driving order signal and a heater driving pulse signal provided separately, and are discharged as ink droplets.
The recording buffer 105a is provided on a synchronous dynamic random access memory (SDRAM) which has a burst reading function. As shown in FIG. 6(i), the recording data are stored in consecutive addresses in the direction of nozzle array (i.e., the y-direction in the figure). Hereinafter, such recording buffer configuration will be referred to as a raster-format recording buffer.
When the recording data is read from the recording buffer 105a by direct memory access (DMA), by designating a read start address A, the address is automatically incremented using the burst reading function of the SDRAM. That is, the data of eight-word portion are DMA read from address A, A+2, A+4, A+6, A+8, A+12, and A+14 at high speed in the direction of the nozzle array. This state is shown in FIG. 6(ii).
In addition, when the data are to be read in the direction of the next nozzle, the data of eight-word portion can be DMA read from consecutive addresses by setting the read start address at A+16. By repeating the DMA reading while updating the read start address of the recording buffer 105a for the entire recording head length (i.e., the entire nozzle number), 16 columns of data can be read out at once.
Furthermore, in the case where the read start address is updated in the scanning direction of the recording head 1 (i.e., in the x-direction in the figure), the read start address is changed to A+B and the reading is performed in the same manner. Here, “B” is a predetermined offset value. The read start address and the offset value are designated by setting a fixed value to a specific register. The register value of the read start address is updated sequentially.
The data of 16 columns that are read out, are stored in a SRAM (1) 106. Here, the data are converted in accordance with the format of the recording head 1 so that recording data can be read out column by column (from column (1) to column (16)), and are stored (refer to FIG. 6 (iii)).
In FIG. 6 (iii), the recording data of one column (column (1)) are read out from the address a, a+1, a+2, and a+3 of the SRAM (1) 106.
FIG. 8 shows a drive circuit for driving the recording head 1. The recording head is controlled by a serial-format recording data signal, a head clock signal, a latch signal for latching data, a block enable signal, and a heater driving pulse signal.
The block enable signal is a signal for each block configured by a plurality of recording head nozzles. The heater driving pulse signal controls driving of the discharging heater provided in the recording head.
In FIG. 8, the recording head drives the 256 heaters (recording elements) 806 dividing them into 16 blocks (one block consisting of 16 heaters), and 16 heaters are driven in each block. The recording data of one column read out from SRAM (1) 106 are rearranged for each block. Here, for example, block 0 is configured of SEG 0, SEG 16, . . . , SEG 240. Block 1 is configured of SEG 1, SEG 17, . . . , SEG 241. Blocks 2 to 15 are similarly configured. Thus, each block is configured of 16 bits.
The rearranged recording data are serially transferred to the recording head 1 by the head clock signal. The recording data received by a 16-bit shift register 801, are latched at the leading edge of the latch signal in latch 802. The block designation is indicated by four block enable signals, and the expanded heater 806 of the designated block is selected at the decoder 803.
Only the segment of the heater 806 designated by both the block enable signal and the recording data signal are driven by the actual heater driving pulse signal (AND gate 805), and the recording is conducted by discharged ink.
The block driving order is determined and controlled so as to minimize the variation in the landing position of the ink that arises from the variation of nozzles made in the manufacturing process.
In addition, in recent years, there is a means for reducing block enable signals by which block enable data converted to serial data is added to the serial signal of the recording data.
FIG. 9 illustrates the relation between the head clock signal and the recording data signal in the case where the recording data to which block data is added, is transferred.
In FIG. 9, the recording data are transferred to the recording head, at the leading edge and the trailing edge of the head clock signal. For example, in the case where the data of block 1 are transferred, the data of SEG 0 as data 0, the data of SEG 16 as data 1, . . . , and data of SEG 240 as data 15 are transferred in FIG. 9. The blocks are designated by 4 bits, BE0, BE1, BE2, and BE3, which follows the above data. For example, block 1 is selected by transferring data in the order of “1”, “0”, “0”, “0”.
In the case where the recording head is not correctly mounted on the carriage, or the ink discharging port is arranged so as to be tilted relative to the conveying direction of the recording medium, the recording position may become misaligned, and the desired recording result may not be obtained. In particular, the misalignment of the recording positions caused by tilting of the recording head may be more noticeable in color printing in which a plurality of colors are overlapped to form an image.
There is a case where the recording head is mounted on the carriage in a tilt (inclination) state due to incorrect mounting by a user. In addition, there is a case where a recording head is mounted whose nozzle array is previously tilted. In such a case, information about the tilt (inclination) of the nozzle array is obtained from the adjustment mode and the like, and the recording head is controlled based on the information.
Furthermore, there may be a case where correction required exceeds one column because a number of nozzles in the recording head is increased or the length of the nozzle array is extended.
In such a case, the nozzle arrays of the recording head are separated into blocks, for example, that of 32-nozzles, and a window signal is provided to each block. One recording head is regarded as a plurality of recording heads and the timing of the window signal is displaced. Thus, for each block, control is performed to correct the print timing in one-column trigger unit.
FIG. 10 shows a diagram to illustrate a control method for correcting a tilted recording head in one-column trigger unit. It should be noted that the degree of tilt is not limited to that as shown in FIG. 10. In FIG. 10, the recording head includes 256 nozzles and is set on the carriage so as to perform printing in a position displaced by one-column trigger of time in a unit of 64 nozzles.
In order to form a high-quality image, the tilt of such recording head is corrected such that window (1) to window (8) signals are provided in advance to each of the blocks (1) to (8), that include 32 nozzles respectively.
Since the recording head is tilted, if the window (1) to window (8) signals are opened (enabled) at the same timing, the data of block (3), for example, causes ink to be discharged earlier by one-column trigger as compared to the data of block (1).
Accordingly, the window (3) signal is opened one-column trigger (or one-column) later than the window (1) signal. The image made under such control looks as if it is formed by the ink discharged by a recording head with a nozzle array that is not tilted.
That is, one recording head is regarded as an assembly of a plurality of recording heads and each head is controlled independently so that the tilt of the recording head is corrected.
FIG. 11 shows a table illustrating the data reading position in the SRAM (1) 106 in the case where the control for correcting the tilt of the recording head shown in FIG. 10 is performed in the configuration shown in FIG. 5.
In FIG. 11, a to p on the horizontal axis and 0 to 7 on the vertical axis are indexes for indicating the addresses of the SRAM (1) 106. a0, a1, . . . , to a7 are arranged as consecutive addresses, and b0, b1, . . . , to b7, c0, c1, . . . , to c7, p0, p1, . . . to p7 are also arranged as consecutive addresses. These addresses correspond to the conveying direction of the recording medium, or in other words, to the direction perpendicular to the scanning direction of the recording head.
In addition, the values written in each box is the data stored in that address. That is, data a is stored in address a, data a+1 in address a+1, . . . , and data p+7 in address a+7.
In the case where the recording head (or the nozzle array) is tilted as in FIG. 10, when the recording data of one column are readout by accessing the consecutive addresses (such as a, a+1, a+2, a+3, a+4, a+5, a+6, and a+7) from SRAM (1) 106 in FIG. 5, the ink lands on the recording medium in accordance with the tilt of the recording head, and the dots become tilted.
Therefore, in order to prevent the dots from becoming tilted, the addresses are accessed in the order of d, d+1, c+2, c+3, b+4, b+5, a+6, and a+7 to read out data of one column.
However, in the configuration shown in FIG. 5, four triggers (or timings) are used in reading out data of one column stored in SRAM (1) 106 because each column position of the addresses d and d+1, addresses c+2 and c+3, addresses b+4 and b+5, and addresses a+6 and a+7 is different.
If the time between the triggers is T, the time for writing 16 columns of data is W, and the number of recording heads is N, for one bank as described before, the following relation should hold:16T>NW  (Equation 1)
However, in the case where the data that are originally one column, are read over a plurality of column triggers in order to correct the tilt of the recording head, the equation 1 should be changed as follows if there is a tilt of three columns as in FIG. 10:(16−3)T=13T>NW  (Equation 2)According to this equation, in the case where the number of recording head N becomes large, or the number of nozzles in one array increases, that is, W becomes large, there will not be enough time for reading out the data which is transferred to the recording head.
In another words, in the configuration of FIG. 5, the data amount (or the number of columns) that can be transferred from SRAM (1) 106 to the recording head 1 with respect to one bank, corresponds to 16 columns if the tilt is zero. However, if the tilt is three columns, data of only 13 columns can be read out from one bank.
Therefore, in the configuration of FIG. 5, the data amount that can be read out from one bank decreases as the tilt increases. The step of transferring data from SRAM (1) 106 to the recording head 1 becomes a bottleneck in the process of transferring data from the recording buffer 105a to the recording head 1.
In addition, in the case where the timing of storing into SRAM (1) 106 is set independently in response to the tilt of the recording head 1, the address management of the reading address in the recording buffer 105a and the like are also conducted independently so that relevant control becomes cumbersome. Alternatively, in the case where the timing of reading out from SRAM (1) 106 is set independently in response to the tilt of the recording head 1, the control becomes cumbersome also.